Network Working Group E. Ivov
Internet-Draft Atlassian
Intended status: Standards Track E. Rescorla
Expires: October 17, 2018 RTFM, Inc.
J. Uberti
Google
P. Saint-Andre
Mozilla
April 15, 2018
Trickle ICE: Incremental Provisioning of Candidates for the Interactive
Connectivity Establishment (ICE) Protocol
draft-ietf-ice-trickle-21
Abstract
This document describes "Trickle ICE", an extension to the
Interactive Connectivity Establishment (ICE) protocol that enables
ICE agents to begin connectivity checks while they are still
gathering candidates, by incrementally exchanging candidates over
time instead of all at once. This method can considerably accelerate
the process of establishing a communication session.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 17, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Determining Support for Trickle ICE . . . . . . . . . . . . . 6
4. Generating the Initial ICE Description . . . . . . . . . . . 7
5. Handling the Initial ICE Description and Generating the
Initial ICE Response . . . . . . . . . . . . . . . . . . . . 7
6. Handling the Initial ICE Response . . . . . . . . . . . . . . 8
7. Forming Check Lists . . . . . . . . . . . . . . . . . . . . . 8
8. Performing Connectivity Checks . . . . . . . . . . . . . . . 8
9. Gathering and Conveying Newly Gathered Local Candidates . . . 9
10. Pairing Newly Gathered Local Candidates . . . . . . . . . . . 10
11. Receiving Trickled Candidates . . . . . . . . . . . . . . . . 11
12. Inserting Trickled Candidate Pairs into a Check List . . . . 12
13. Generating an End-of-Candidates Indication . . . . . . . . . 16
14. Receiving an End-of-Candidates Indication . . . . . . . . . . 17
15. Subsequent Exchanges and ICE Restarts . . . . . . . . . . . . 18
16. Half Trickle . . . . . . . . . . . . . . . . . . . . . . . . 18
17. Preserving Candidate Order while Trickling . . . . . . . . . 19
18. Requirements for Using Protocols . . . . . . . . . . . . . . 20
19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
20. Security Considerations . . . . . . . . . . . . . . . . . . . 21
21. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
22. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
22.1. Normative References . . . . . . . . . . . . . . . . . . 22
22.2. Informative References . . . . . . . . . . . . . . . . . 22
Appendix A. Interaction with Regular ICE . . . . . . . . . . . . 23
Appendix B. Interaction with ICE Lite . . . . . . . . . . . . . 25
Appendix C. Changes from Earlier Versions . . . . . . . . . . . 26
C.1. Changes from draft-ietf-ice-trickle-20 . . . . . . . . . 26
C.2. Changes from draft-ietf-ice-trickle-19 . . . . . . . . . 26
C.3. Changes from draft-ietf-ice-trickle-18 . . . . . . . . . 26
C.4. Changes from draft-ietf-ice-trickle-17 . . . . . . . . . 27
C.5. Changes from draft-ietf-ice-trickle-16 . . . . . . . . . 27
C.6. Changes from draft-ietf-ice-trickle-15 . . . . . . . . . 27
C.7. Changes from draft-ietf-ice-trickle-14 . . . . . . . . . 27
C.8. Changes from draft-ietf-ice-trickle-13 . . . . . . . . . 27
C.9. Changes from draft-ietf-ice-trickle-12 . . . . . . . . . 27
C.10. Changes from draft-ietf-ice-trickle-11 . . . . . . . . . 28
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C.11. Changes from draft-ietf-ice-trickle-10 . . . . . . . . . 28
C.12. Changes from draft-ietf-ice-trickle-09 . . . . . . . . . 28
C.13. Changes from draft-ietf-ice-trickle-08 . . . . . . . . . 28
C.14. Changes from draft-ietf-ice-trickle-07 . . . . . . . . . 28
C.15. Changes from draft-ietf-ice-trickle-06 . . . . . . . . . 28
C.16. Changes from draft-ietf-ice-trickle-05 . . . . . . . . . 28
C.17. Changes from draft-ietf-ice-trickle-04 . . . . . . . . . 29
C.18. Changes from draft-ietf-ice-trickle-03 . . . . . . . . . 29
C.19. Changes from draft-ietf-ice-trickle-02 . . . . . . . . . 29
C.20. Changes from draft-ietf-ice-trickle-01 . . . . . . . . . 29
C.21. Changes from draft-ietf-ice-trickle-00 . . . . . . . . . 29
C.22. Changes from draft-mmusic-trickle-ice-02 . . . . . . . . 29
C.23. Changes from draft-ivov-01 and draft-mmusic-00 . . . . . 30
C.24. Changes from draft-ivov-00 . . . . . . . . . . . . . . . 30
C.25. Changes from draft-rescorla-01 . . . . . . . . . . . . . 31
C.26. Changes from draft-rescorla-00 . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction
The Interactive Connectivity Establishment (ICE) protocol
[rfc5245bis] describes how an ICE agent gathers candidates, exchanges
candidates with a peer ICE agent, and creates candidate pairs. Once
the pairs have been gathered, the ICE agent will perform connectivity
checks, and eventually nominate and select pairs that will be used
for sending and receiving data within a communication session.
Following the procedures in [rfc5245bis] can lead to somewhat lengthy
establishment times for communication sessions, because candidate
gathering often involves querying STUN servers [RFC5389] and
allocating relayed candidates using TURN servers [RFC5766]. Although
many ICE procedures can be completed in parallel, the pacing
requirements from [rfc5245bis] still need to be followed.
This document defines "Trickle ICE", a supplementary mode of ICE
operation in which candidates can be exchanged incrementally as soon
as they become available (and simultaneously with the gathering of
other candidates). Connectivity checks can also start as soon as
candidate pairs have been created. Because Trickle ICE enables
candidate gathering and connectivity checks to be done in parallel,
the method can considerably accelerate the process of establishing a
communication session.
This document also defines how to discover support for Trickle ICE,
how the procedures in [rfc5245bis] are modified or supplemented when
using Trickle ICE, and how a Trickle ICE agent can interoperate with
an ICE agent compliant to [rfc5245bis].
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This document does not define any protocol-specific usage of Trickle
ICE. Instead, protocol-specific details for Trickle ICE are defined
in separate usage documents. Examples of such documents are
[I-D.ietf-mmusic-trickle-ice-sip] (which defines usage with the
Session Initiation Protocol (SIP) [RFC3261] and the Session
Description Protocol [RFC3261]) and [XEP-0176] (which defines usage
with XMPP [RFC6120]). However, some of the examples in the document
use SDP and the offer/answer model [RFC3264] to explain the
underlying concepts.
The following diagram illustrates a successful Trickle ICE exchange
with a using protocol that follows the offer/answer model:
Alice Bob
| Offer |
|---------------------------------------------->|
| Additional Candidates |
|---------------------------------------------->|
| Answer |
||
|<========== CONNECTION ESTABLISHED ===========>|
Figure 1: Flow
The main body of this document is structured to describe the behavior
of Trickle ICE agents in roughly the order of operations and
interactions during an ICE session:
1. Determining support for trickle ICE
2. Generating the initial ICE description
3. Handling the initial ICE description and generating the initial
ICE response
4. Handling the initial ICE response
5. Forming check lists, pruning candidates, performing connectivity
checks, etc.
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6. Gathering and conveying candidates after the initial ICE
description and response
7. Handling inbound trickled candidates
8. Generating and handling the end-of-candidates indication
9. Handling ICE restarts
There is quite a bit of operational experience with the technique
behind Trickle ICE, going back as far as 2005 (when the XMPP Jingle
extension defined a "dribble mode" as specified in [XEP-0176]); this
document incorporates feedback from those who have implemented and
deployed the technique over the years.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
This specification makes use of all terminology defined for
Interactive Connectivity Establishment in [rfc5245bis]. In addition,
it defines the following terms:
Full Trickle: The typical mode of operation for Trickle ICE agents,
in which the initial ICE description can include any number of
candidates (even zero candidates) and does not need to include a
full generation of candidates as in half trickle.
Generation: All of the candidates conveyed within an ICE session.
Half Trickle: A Trickle ICE mode of operation in which the initiator
gathers a full generation of candidates strictly before creating
and conveying the initial ICE description. Once conveyed, this
candidate information can be processed by regular ICE agents,
which do not require support for Trickle ICE. It also allows
Trickle ICE capable responders to still gather candidates and
perform connectivity checks in a non-blocking way, thus providing
roughly "half" the advantages of Trickle ICE. The half trickle
mechanism is mostly meant for use when the responder's support for
Trickle ICE cannot be confirmed prior to conveying the initial ICE
description.
ICE Description: Any attributes related to the ICE session (not
candidates) required to configure an ICE agent. These include but
are not limited to the username fragment, password, and other
attributes.
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Trickled Candidates: Candidates that a Trickle ICE agent conveys
after conveying the initial ICE description or responding to the
initial ICE description, but within the same ICE session.
Trickled candidates can be conveyed in parallel with candidate
gathering and connectivity checks.
Trickling: The act of incrementally conveying trickled candidates.
Empty Check List: A check list that initially does not contain any
candidate pairs because they will be incrementally added as they
are trickled. (This scenario does not arise with a regular ICE
agent, because all candidate pairs are known when the agent
creates the check list set).
3. Determining Support for Trickle ICE
To fully support Trickle ICE, using protocols SHOULD incorporate one
of the following mechanisms so that implementations can determine
whether Trickle ICE is supported:
1. Provide a capabilities discovery method so that agents can verify
support of Trickle ICE prior to initiating a session (XMPP's
Service Discovery [XEP-0030] is one such mechanism).
2. Make support for Trickle ICE mandatory so that user agents can
assume support.
If a using protocol does not provide a method of determining ahead of
time whether Trickle ICE is supported, agents can make use of the
half trickle procedure described in Section 16.
Prior to conveying the initial ICE description, agents that implement
using protocols that support capabilities discovery can attempt to
verify whether or not the remote party supports Trickle ICE. If an
agent determines that the remote party does not support Trickle ICE,
it MUST fall back to using regular ICE or abandon the entire session.
Even if a using protocol does not include a capabilities discovery
method, a user agent can provide an indication within the ICE
description that it supports Trickle ICE by communicating an ICE
option of 'trickle'. This token MUST be provided either at the
session level or, if at the data stream level, for every data stream
(an agent MUST NOT specify Trickle ICE support for some data streams
but not others). Note: The encoding of the 'trickle' ICE option, and
the message(s) used to carry it to the peer, are protocol specific;
for instance, the encoding for the Session Description Protocol (SDP)
[RFC4566] is defined in [I-D.ietf-mmusic-trickle-ice-sip].
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Dedicated discovery semantics and half trickle are needed only prior
to initiation of an ICE session. After an ICE session is established
and Trickle ICE support is confirmed for both parties, either agent
can use full trickle for subsequent exchanges (see also Section 15).
4. Generating the Initial ICE Description
An ICE agent can start gathering candidates as soon as it has an
indication that communication is imminent (e.g., a user interface cue
or an explicit request to initiate a communication session). Unlike
in regular ICE, in Trickle ICE implementations do not need to gather
candidates in a blocking manner. Therefore, unless half trickle is
being used, the user experience is improved if the initiating agent
generates and transmits its initial ICE description as early as
possible (thus enabling the remote party to start gathering and
trickling candidates).
An initiator MAY include any mix of candidates when conveying the
initial ICE description. This includes the possibility of conveying
all the candidates the initiator plans to use (as in half trickle),
conveying only a publicly-reachable IP address (e.g., a candidate at
a data relay that is known to not be behind a firewall), or conveying
no candidates at all (in which case the initiator can obtain the
responder's initial candidate list sooner and the responder can begin
candidate gathering more quickly).
For candidates included in the initial ICE description, the methods
for calculating priorities and foundations, determining redundancy of
candidates, and the like work just as in regular ICE [rfc5245bis].
5. Handling the Initial ICE Description and Generating the Initial ICE
Response
When a responder receives the initial ICE description, it will first
check if the ICE description or initiator indicates support for
Trickle ICE as explained in Section 3. If not, the responder MUST
process the initial ICE description according to regular ICE
procedures [rfc5245bis] (or, if no ICE support is detected at all,
according to relevant processing rules for the using protocol, such
as offer/answer processing rules [RFC3264]). However, if support for
Trickle ICE is confirmed, a responder will automatically assume
support for regular ICE as well.
If the initial ICE description indicates support for Trickle ICE, the
responder will determine its role and start gathering and
prioritizing candidates; while doing so, it will also respond by
conveying an initial ICE response, so that both the initiator and the
responder can form check lists and begin connectivity checks.
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A responder can respond to the initial ICE description at any point
while gathering candidates. The initial ICE response MAY contain any
set of candidates, including all candidates or no candidates. (The
benefit of including no candidates is to convey the initial ICE
response as quickly as possible, so that both parties can consider
the ICE session to be under active negotiation as soon as possible.)
As noted in Section 3, in using protocols that use SDP the initial
ICE response can indicate support for Trickle ICE by including a
token of "trickle" in the ice-options attribute.
6. Handling the Initial ICE Response
When processing the initial ICE response, the initiator follows
regular ICE procedures to determine its role, after which it forms
check lists (Section 7) and performs connectivity checks (Section 8).
7. Forming Check Lists
According to regular ICE procedures [rfc5245bis], in order for
candidate pairing to be possible and for redundant candidates to be
pruned, the candidates would need to be provided in the initial ICE
description and initial ICE response. By contrast, under Trickle ICE
check lists can be empty until candidates are conveyed or received.
Therefore a Trickle ICE agent handles check list formation and
candidate pairing in a slightly different way than a regular ICE
agent: the agent still forms the check lists, but it populates a
given check list only after it actually has candidate pairs for that
check list. Every check list is initially placed in the Running
state, even if the check list is empty (this is consistent with
Section 6.1.2.1 of [rfc5245bis]).
8. Performing Connectivity Checks
As specified in [rfc5245bis], whenever timer Ta fires, only check
lists in the Running state will be picked when scheduling
connectivity checks for candidate pairs. Therefore, a Trickle ICE
agent MUST keep each check list in the Running state as long as it
expects candidate pairs to be incrementally added to the check list.
After that, the check list state is set according to the procedures
in [rfc5245bis].
Whenever timer Ta fires and an empty check list is picked, no action
is performed for the list. Without waiting for timer Ta to expire
again, the agent selects the next check list in the Running state, in
accordance with Section 6.1.4.2 of [rfc5245bis].
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Section 7.2.5.3.3 of [rfc5245bis] requires that agents update check
lists and timer states upon completing a connectivity check
transaction. During such an update, regular ICE agents would set the
state of a check list to Failed if both of the following two
conditions are satisfied:
o all of the pairs in the check list are either in the Failed state
or Succeeded state; and
o there is not a pair in the valid list for each component of the
data stream.
With Trickle ICE, the above situation would often occur when
candidate gathering and trickling are still in progress, even though
it is quite possible that future checks will succeed. For this
reason, Trickle ICE agents add the following conditions to the above
list:
o all candidate gathering has completed and the agent is not
expecting to discover any new local candidates; and
o the remote agent has conveyed an end-of-candidates indication for
that check list as described in Section 13.
9. Gathering and Conveying Newly Gathered Local Candidates
After Trickle ICE agents have conveyed initial ICE descriptions and
initial ICE responses, they will most likely continue gathering new
local candidates as STUN, TURN, and other non-host candidate
gathering mechanisms begin to yield results. Whenever an agent
discovers such a new candidate it will compute its priority, type,
foundation, and component ID according to regular ICE procedures.
The new candidate is then checked for redundancy against the existing
list of local candidates. If its transport address and base match
those of an existing candidate, it will be considered redundant and
will be ignored. This would often happen for server reflexive
candidates that match the host addresses they were obtained from
(e.g., when the latter are public IPv4 addresses). Contrary to
regular ICE, Trickle ICE agents will consider the new candidate
redundant regardless of its priority.
Next the agent "trickles" the newly discovered candidate(s) to the
remote agent. The actual delivery of the new candidates is handled
by a using protocol such as SIP or XMPP. Trickle ICE imposes no
restrictions on the way this is done (e.g., some using protocols
might choose not to trickle updates for server reflexive candidates
and instead rely on the discovery of peer reflexive ones).
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When candidates are trickled, the using protocol MUST deliver each
candidate (and any end-of-candidates indication as described in
Section 13) to the receiving Trickle ICE implementation exactly once
and in the same order it was conveyed. If the using protocol
provides any candidate retransmissions, they need to be hidden from
the ICE implementation.
Also, candidate trickling needs to be correlated to a specific ICE
session, so that if there is an ICE restart, any delayed updates for
a previous session can be recognized as such and ignored by the
receiving party. For example, using protocols that signal candidates
via SDP might include a Username Fragment value in the corresponding
a=candidate line, such as:
a=candidate:1 1 UDP 2130706431 2001:db8::1 5000 typ host ufrag 8hhY
Or, as another example, WebRTC implementations might include a
Username Fragment in the JavaScript objects that represent
candidates.
Note: The using protocol needs to provide a mechanism for both
parties to indicate and agree on the ICE session in force (as
identified by the Username Fragment and Password combination) so that
they have a consistent view of which candidates are to be paired.
This is especially important in the case of ICE restarts (see
Section 15).
Note: A using protocol might prefer not to trickle server reflexive
candidates to entities that are known to be publicly accessible and
where sending a direct STUN binding request is likely to reach the
destination faster than the trickle update that travels through the
signaling path.
10. Pairing Newly Gathered Local Candidates
As a Trickle ICE agent gathers local candidates, it needs to form
candidate pairs; this works as described in the ICE specification
[rfc5245bis], with the following provisos:
1. A Trickle ICE agent MUST NOT pair a local candidate until it has
been trickled to the remote party.
2. Once the agent has conveyed the local candidate to the remote
party, the agent checks if any remote candidates are currently
known for this same stream and component. If not, the agent
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merely adds the new candidate to the list of local candidates
(without pairing it).
3. Otherwise, if the agent has already learned of one or more remote
candidates for this stream and component, it attempts to pair the
new local candidate as described in the ICE specification
[rfc5245bis].
4. If a newly formed pair has a local candidate whose type is server
reflexive, the agent MUST replace the local candidate with its
base before completing the relevant redundancy tests.
5. The agent prunes redundant pairs by following the rules in
Section 6.1.2.4 of [rfc5245bis], but checks existing pairs only
if they have a state of Waiting or Frozen; this avoids removal of
pairs for which connectivity checks are in flight (a state of In-
Progress) or for which connectivity checks have already yielded a
definitive result (a state of Succeeded or Failed).
6. If after the relevant redundancy tests the check list where the
pair is to be added already contains the maximum number of
candidate pairs (100 by default as per [rfc5245bis]), the agent
SHOULD discard any pairs in the Failed state to make room for the
new pair. If there are no such pairs, the agent SHOULD discard a
pair with a lower priority than the new pair in order to make
room for the new pair, until the number of pairs is equal to the
maximum number of pairs. This processing is consistent with
Section 6.1.2.5 of [rfc5245bis].
11. Receiving Trickled Candidates
At any time during an ICE session, a Trickle ICE agent might receive
new candidates from the remote agent, from which it will attempt to
form a candidate pair; this works as described in the ICE
specification [rfc5245bis], with the following provisos:
1. The agent checks if any local candidates are currently known for
this same stream and component. If not, the agent merely adds
the new candidate to the list of remote candidates (without
pairing it).
2. Otherwise, if the agent has already gathered one or more local
candidates for this stream and component, it attempts to pair the
new remote candidate as described in the ICE specification
[rfc5245bis].
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3. If a newly formed pair has a local candidate whose type is server
reflexive, the agent MUST replace the local candidate with its
base before completing the redundancy check in the next step.
4. The agent prunes redundant pairs as described below, but checks
existing pairs only if they have a state of Waiting or Frozen;
this avoids removal of pairs for which connectivity checks are in
flight (a state of In-Progress) or for which connectivity checks
have already yielded a definitive result (a state of Succeeded or
Failed).
A. If the agent finds a redundancy between two pairs and one of
those pairs contains a newly received remote candidate whose
type is peer reflexive, the agent SHOULD discard the pair
containing that candidate, set the priority of the existing
pair to the priority of the discarded pair, and re-sort the
check list. (This policy helps to eliminate problems with
remote peer reflexive candidates for which a STUN binding
request is received before signaling of the candidate is
trickled to the receiving agent, such as a different view of
pair priorities between the local agent and the remote agent,
since the same candidate could be perceived as peer reflexive
by one agent and as server reflexive by the other agent.)
B. The agent then applies the rules defined in Section 6.1.2.4
of [rfc5245bis].
5. If after the relevant redundancy tests the check list where the
pair is to be added already contains the maximum number of
candidate pairs (100 by default as per [rfc5245bis]), the agent
SHOULD discard any pairs in the Failed state to make room for the
new pair. If there are no such pairs, the agent SHOULD discard a
pair with a lower priority than the new pair in order to make
room for the new pair, until the number of pairs is equal to the
maximum number of pairs. This processing is consistent with
Section 6.1.2.5 of [rfc5245bis].
12. Inserting Trickled Candidate Pairs into a Check List
After a local agent has trickled a candidate and formed a candidate
pair from that local candidate (Section 9), or after a remote agent
has received a trickled candidate and formed a candidate pair from
that remote candidate (Section 11), a Trickle ICE agent adds the new
candidate pair to a check list as defined in this section.
As an aid to understanding the procedures defined in this section,
consider the following tabular representation of all check lists in
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an agent (note that initially for one of the foundations, i.e., f5,
there are no candidate pairs):
+-----------------+------+------+------+------+------+
| | f1 | f2 | f3 | f4 | f5 |
+-----------------+------+------+------+------+------+
| s1 (Audio.RTP) | F | F | F | | |
+-----------------+------+------+------+------+------+
| s2 (Audio.RTCP) | F | F | F | F | |
+-----------------+------+------+------+------+------+
| s3 (Video.RTP) | F | | | | |
+-----------------+------+------+------+------+------+
| s4 (Video.RTCP) | F | | | | |
+-----------------+------+------+------+------+------+
Figure 2: Example of Check List State
Each row in the table represents a component for a given data stream
(e.g., s1 and s2 might be the RTP and RTCP components for audio) and
thus a single check list in the check list set. Each column
represents one foundation. Each cell represents one candidate pair.
In the tables shown in this section, "F" stands for "frozen", "W"
stands for "waiting", and "S" stands for "succeeded"; in addition,
"^^" is used to notate newly-added candidate pairs.
When an agent commences ICE processing, in accordance with
Section 6.1.2.6 of [rfc5245bis], for each foundation it will unfreeze
the pair with the lowest component ID and, if the component IDs are
equal, with the highest priority (this is the topmost candidate pair
in every column). This initial state is shown in the following
table.
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+-----------------+------+------+------+------+------+
| | f1 | f2 | f3 | f4 | f5 |
+-----------------+------+------+------+------+------+
| s1 (Audio.RTP) | W | W | W | | |
+-----------------+------+------+------+------+------+
| s2 (Audio.RTCP) | F | F | F | W | |
+-----------------+------+------+------+------+------+
| s3 (Video.RTP) | F | | | | |
+-----------------+------+------+------+------+------+
| s4 (Video.RTCP) | F | | | | |
+-----------------+------+------+------+------+------+
Figure 3: Initial Check List State
Then, as the checks proceed (see Section 7.2.5.4 of [rfc5245bis]),
for each pair that enters the Succeeded state (denoted here by "S"),
the agent will unfreeze all pairs for all data streams with the same
foundation (e.g., if the pair in column 1, row 1 succeeds then the
agent will unfreeze the pair in column 1, rows 2, 3, and 4).
+-----------------+------+------+------+------+------+
| | f1 | f2 | f3 | f4 | f5 |
+-----------------+------+------+------+------+------+
| s1 (Audio.RTP) | S | W | W | | |
+-----------------+------+------+------+------+------+
| s2 (Audio.RTCP) | W | F | F | W | |
+-----------------+------+------+------+------+------+
| s3 (Video.RTP) | W | | | | |
+-----------------+------+------+------+------+------+
| s4 (Video.RTCP) | W | | | | |
+-----------------+------+------+------+------+------+
Figure 4: Check List State with Succeeded Candidate Pair
Trickle ICE preserves all of these rules as they apply to "static"
check list sets. This implies that if a Trickle ICE agent were to
begin connectivity checks with all of its pairs already present, the
way that pair states change is indistinguishable from that of a
regular ICE agent.
Of course, the major difference with Trickle ICE is that check list
sets can be dynamically updated because candidates can arrive after
connectivity checks have started. When this happens, an agent sets
the state of the newly formed pair as described below.
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Rule 1: If the newly formed pair has the lowest component ID and, if
the component IDs are equal, the highest priority of any candidate
pair for this foundation (i.e., if it is the topmost pair in the
column), set the state to Waiting. For example, this would be the
case if the newly formed pair were placed in column 5, row 1. This
rule is consistent with Section 6.1.2.6 of [rfc5245bis].
+-----------------+------+------+------+------+------+
| | f1 | f2 | f3 | f4 | f5 |
+-----------------+------+------+------+------+------+
| s1 (Audio.RTP) | S | W | W | | ^W^ |
+-----------------+------+------+------+------+------+
| s2 (Audio.RTCP) | W | F | F | W | |
+-----------------+------+------+------+------+------+
| s3 (Video.RTP) | W | | | | |
+-----------------+------+------+------+------+------+
| s4 (Video.RTCP) | W | | | | |
+-----------------+------+------+------+------+------+
Figure 5: Check List State with Newly Formed Pair, Rule 1
Rule 2: If there is at least one pair in the Succeeded state for this
foundation, set the state to Waiting. For example, this would be the
case if the pair in column 5, row 1 succeeded and the newly formed
pair were placed in column 5, row 2. This rule is consistent with
Section 7.2.5.3.3 of [rfc5245bis].
+-----------------+------+------+------+------+------+
| | f1 | f2 | f3 | f4 | f5 |
+-----------------+------+------+------+------+------+
| s1 (Audio.RTP) | S | W | W | | S |
+-----------------+------+------+------+------+------+
| s2 (Audio.RTCP) | W | F | F | W | ^W^ |
+-----------------+------+------+------+------+------+
| s3 (Video.RTP) | W | | | | |
+-----------------+------+------+------+------+------+
| s4 (Video.RTCP) | W | | | | |
+-----------------+------+------+------+------+------+
Figure 6: Check List State with Newly Formed Pair, Rule 2
Rule 3: In all other cases, set the state to Frozen. For example,
this would be the case if the newly formed pair were placed in column
3, row 3.
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+-----------------+------+------+------+------+------+
| | f1 | f2 | f3 | f4 | f5 |
+-----------------+------+------+------+------+------+
| s1 (Audio.RTP) | S | W | W | | S |
+-----------------+------+------+------+------+------+
| s2 (Audio.RTCP) | W | F | F | W | W |
+-----------------+------+------+------+------+------+
| s3 (Video.RTP) | W | | ^F^ | | |
+-----------------+------+------+------+------+------+
| s4 (Video.RTCP) | W | | | | |
+-----------------+------+------+------+------+------+
Figure 7: Check List State with Newly Formed Pair, Rule 3
13. Generating an End-of-Candidates Indication
Once all candidate gathering is completed or expires for an ICE
session associated with a specific data stream, the agent will
generate an "end-of-candidates" indication for that session and
convey it to the remote agent via the signaling channel. Although
the exact form of the indication depends on the using protocol, the
indication MUST specify the generation (Username Fragment and
Password combination) so that an agent can correlate the end-of-
candidates indication with a particular ICE session. The indication
can be conveyed in the following ways:
o As part of an initiation request (which would typically be the
case with the initial ICE description for half trickle)
o Along with the last candidate an agent can send for a stream
o As a standalone notification (e.g., after STUN Binding requests or
TURN Allocate requests to a server time out and the agent is no
longer actively gathering candidates)
Conveying an end-of-candidates indication in a timely manner is
important in order to avoid ambiguities and speed up the conclusion
of ICE processing. In particular:
o A controlled Trickle ICE agent SHOULD convey an end-of-candidates
indication after it has completed gathering for a data stream,
unless ICE processing terminates before the agent has had a chance
to complete gathering.
o A controlling agent MAY conclude ICE processing prior to conveying
end-of-candidates indications for all streams. However, it is
RECOMMENDED for a controlling agent to convey end-of-candidates
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indications whenever possible for the sake of consistency and to
keep middleboxes and controlled agents up-to-date on the state of
ICE processing.
When conveying an end-of-candidates indication during trickling
(rather than as a part of the initial ICE description or a response
thereto), it is the responsibility of the using protocol to define
methods for associating the indication with one or more specific data
streams.
An agent MAY also choose to generate an end-of-candidates indication
before candidate gathering has actually completed, if the agent
determines that gathering has continued for more than an acceptable
period of time. However, an agent MUST NOT convey any more
candidates after it has conveyed an end-of-candidates indication.
When performing half trickle, an agent SHOULD convey an end-of-
candidates indication together with its initial ICE description
unless it is planning to potentially trickle additional candidates
(e.g., in case the remote party turns out to support Trickle ICE).
After an agent conveys the end-of-candidates indication, it will
update the state of the corresponding check list as explained in
Section 8. Past that point, an agent MUST NOT trickle any new
candidates within this ICE session. Therefore, adding new candidates
to the negotiation is possible only through an ICE restart (see
Section 15).
This specification does not override regular ICE semantics for
concluding ICE processing. Therefore, even if end-of-candidates
indications are conveyed, an agent will still need to go through pair
nomination. Also, if pairs have been nominated for components and
data streams, ICE processing MAY still conclude even if end-of-
candidates indications have not been received for all streams. In
all cases, an agent MUST NOT trickle any new candidates within an ICE
session after nomination of a candidate pair as described in
Section 8.1.1 of [rfc5245bis].
14. Receiving an End-of-Candidates Indication
Receiving an end-of-candidates indication enables an agent to update
check list states and, in case valid pairs do not exist for every
component in every data stream, determine that ICE processing has
failed. It also enables an agent to speed up the conclusion of ICE
processing when a candidate pair has been validated but it involves
the use of lower-preference transports such as TURN. In such
situations, an implementation MAY choose to wait and see if higher-
priority candidates are received; in this case the end-of-candidates
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indication provides a notification that such candidates are not
forthcoming.
When an agent receives an end-of-candidates indication for a specific
data stream, it will update the state of the relevant check list as
per Section 8 (which might lead to some check lists being marked as
Failed). If the check list is still in the Running state after the
update, the agent will persist the fact that an end-of-candidates
indication has been received and take it into account in future
updates to the check list.
After an agent has received an end-of-candidates indication, it MUST
ignore any newly received candidates for that data stream or data
session.
15. Subsequent Exchanges and ICE Restarts
Before conveying an end-of-candidates indication, either agent MAY
convey subsequent candidate information at any time allowed by the
using protocol. When this happens, agents will use [rfc5245bis]
semantics (e.g., checking of the Username Fragment and Password
combination) to determine whether or not the new candidate
information requires an ICE restart.
If an ICE restart occurs, the agents can assume that Trickle ICE is
still supported if support was determined previously, and thus can
engage in Trickle ICE behavior as they would in an initial exchange
of ICE descriptions where support was determined through a
capabilities discovery method.
16. Half Trickle
In half trickle, the initiator conveys the initial ICE description
with a usable but not necessarily full generation of candidates.
This ensures that the ICE description can be processed by a regular
ICE responder and is mostly meant for use in cases where support for
Trickle ICE cannot be confirmed prior to conveying the initial ICE
description. The initial ICE description indicates support for
Trickle ICE, so that the responder can respond with something less
than a full generation of candidates and then trickle the rest. The
initial ICE description for half trickle can contain an end-of-
candidates indication, although this is not mandatory because if
trickle support is confirmed then the initiator can choose to trickle
additional candidates before it conveys an end-of-candidates
indication.
The half trickle mechanism can be used in cases where there is no way
for an agent to verify in advance whether a remote party supports
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Trickle ICE. Because the initial ICE description contain a full
generation of candidates, it can thus be handled by a regular ICE
agent, while still allowing a Trickle ICE agent to use the
optimization defined in this specification. This prevents
negotiation from failing in the former case while still giving
roughly half the Trickle ICE benefits in the latter.
Use of half trickle is only necessary during an initial exchange of
ICE descriptions. After both parties have received an ICE
description from their peer, they can each reliably determine Trickle
ICE support and use it for all subsequent exchanges (see Section 15).
In some instances, using half trickle might bring more than just half
the improvement in terms of user experience. This can happen when an
agent starts gathering candidates upon user interface cues that the
user will soon be initiating an interaction, such as activity on a
keypad or the phone going off hook. This would mean that some or all
of the candidate gathering could be completed before the agent
actually needs to convey the candidate information. Because the
responder will be able to trickle candidates, both agents will be
able to start connectivity checks and complete ICE processing earlier
than with regular ICE and potentially even as early as with full
trickle.
However, such anticipation is not always possible. For example, a
multipurpose user agent or a WebRTC web page where communication is a
non-central feature (e.g., calling a support line in case of a
problem with the main features) would not necessarily have a way of
distinguishing between call intentions and other user activity. In
such cases, using full trickle is most likely to result in an ideal
user experience. Even so, using half trickle would be an improvement
over regular ICE because it would result in a better experience for
responders.
17. Preserving Candidate Order while Trickling
One important aspect of regular ICE is that connectivity checks for a
specific foundation and component are attempted simultaneously by
both agents, so that any firewalls or NATs fronting the agents would
whitelist both endpoints and allow all except for the first
("suicide") packets to go through. This is also important to
unfreezing candidates at the right time. While not crucial,
preserving this behavior in Trickle ICE is likely to improve ICE
performance.
To achieve this, when trickling candidates, agents SHOULD respect the
order of components as reflected by their component IDs; that is,
candidates for a given component SHOULD NOT be conveyed prior to
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candidates for a component with a lower ID number within the same
foundation. In addition, candidates SHOULD be paired, following the
procedures in Section 12, in the same order they are conveyed.
For example, the following SDP description contains two components
(RTP and RTCP) and two foundations (host and server reflexive):
v=0
o=jdoe 2890844526 2890842807 IN IP4 10.0.1.1
s=
c=IN IP4 10.0.1.1
t=0 0
a=ice-pwd:asd88fgpdd777uzjYhagZg
a=ice-ufrag:8hhY
m=audio 5000 RTP/AVP 0
a=rtpmap:0 PCMU/8000
a=candidate:1 1 UDP 2130706431 10.0.1.1 5000 typ host
a=candidate:1 2 UDP 2130706431 10.0.1.1 5001 typ host
a=candidate:2 1 UDP 1694498815 192.0.2.3 5000 typ srflx
raddr 10.0.1.1 rport 8998
a=candidate:2 2 UDP 1694498815 192.0.2.3 5001 typ srflx
raddr 10.0.1.1 rport 8998
For this candidate information the RTCP host candidate would not be
conveyed prior to the RTP host candidate. Similarly the RTP server
reflexive candidate would be conveyed together with or prior to the
RTCP server reflexive candidate.
18. Requirements for Using Protocols
In order to fully enable the use of Trickle ICE, this specification
defines the following requirements for using protocols.
o A using protocol SHOULD provide a way for parties to advertise and
discover support for Trickle ICE before an ICE session begins (see
Section 3).
o A using protocol MUST provide methods for incrementally conveying
(i.e., "trickling") additional candidates after conveying the
initial ICE description (see Section 9).
o A using protocol MUST deliver each trickled candidate or end-of-
candidates indication exactly once and in the same order it was
conveyed (see Section 9).
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o A using protocol MUST provide a mechanism for both parties to
indicate and agree on the ICE session in force (see Section 9).
o A using protocol MUST provide a way for parties to communicate the
end-of-candidates indication, which MUST specify the particular
ICE session to which the indication applies (see Section 13).
19. IANA Considerations
IANA is requested to register the following ICE option in the "ICE
Options" sub-registry of the "Interactive Connectivity Establishment
(ICE) registry", following the procedures defined in [RFC6336].
ICE Option: trickle
Contact: IESG, iesg@ietf.org
Change control: IESG
Description: An ICE option of "trickle" indicates support for
incremental communication of ICE candidates.
Reference: RFC XXXX
20. Security Considerations
This specification inherits most of its semantics from [rfc5245bis]
and as a result all security considerations described there apply to
Trickle ICE.
If the privacy implications of revealing host addresses on an
endpoint device are a concern (see for example the discussion in
[I-D.ietf-rtcweb-ip-handling] and in Section 19 of [rfc5245bis]),
agents can generate ICE descriptions that contain no candidates and
then only trickle candidates that do not reveal host addresses (e.g.,
relayed candidates).
21. Acknowledgements
The authors would like to thank Bernard Aboba, Flemming Andreasen,
Rajmohan Banavi, Taylor Brandstetter, Philipp Hancke, Christer
Holmberg, Ari Keranen, Paul Kyzivat, Jonathan Lennox, Enrico Marocco,
Pal Martinsen, Nils Ohlmeier, Thomas Stach, Peter Thatcher, Martin
Thomson, Brandon Williams, and Dale Worley for their reviews and
suggestions on improving this document. Sarah Banks, Roni Even, and
David Mandelberg completed opsdir, genart, and security reviews,
respectively. Thanks also to Ari Keranen and Peter Thatcher in their
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role as chairs, and Ben Campbell in his role as responsible Area
Director.
22. References
22.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, .
[rfc5245bis]
Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", draft-ietf-ice-
rfc5245bis-20 (work in progress), March 2018.
22.2. Informative References
[I-D.ietf-mmusic-trickle-ice-sip]
Ivov, E., Stach, T., Marocco, E., and C. Holmberg, "A
Session Initiation Protocol (SIP) usage for Trickle ICE",
draft-ietf-mmusic-trickle-ice-sip-14 (work in progress),
February 2018.
[I-D.ietf-rtcweb-ip-handling]
Uberti, J. and G. Shieh, "WebRTC IP Address Handling
Requirements", draft-ietf-rtcweb-ip-handling-06 (work in
progress), March 2018.
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
and E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002, .
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002, .
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[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, .
[RFC4787] Audet, F., Ed. and C. Jennings, "Network Address
Translation (NAT) Behavioral Requirements for Unicast
UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
2007, .
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008, .
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766,
DOI 10.17487/RFC5766, April 2010, .
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
March 2011, .
[RFC6336] Westerlund, M. and C. Perkins, "IANA Registry for
Interactive Connectivity Establishment (ICE) Options",
RFC 6336, DOI 10.17487/RFC6336, July 2011,
.
[XEP-0030]
Hildebrand, J., Millard, P., Eatmon, R., and P. Saint-
Andre, "XEP-0030: Service Discovery", XEP XEP-0030, June
2008.
[XEP-0176]
Beda, J., Ludwig, S., Saint-Andre, P., Hildebrand, J.,
Egan, S., and R. McQueen, "XEP-0176: Jingle ICE-UDP
Transport Method", XEP XEP-0176, June 2009.
Appendix A. Interaction with Regular ICE
The ICE protocol was designed to be flexible enough to work in and
adapt to as many network environments as possible. Despite that
flexibility, ICE as specified in [rfc5245bis] does not by itself
support trickle ICE. This section describes how trickling of
candidates interacts with ICE.
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[rfc5245bis] describes the conditions required to update check lists
and timer states while an ICE agent is in the Running state. These
conditions are verified upon transaction completion and one of them
stipulates that:
If there is not a pair in the valid list for each component of the
data stream, the state of the check list is set to Failed.
This could be a problem and cause ICE processing to fail prematurely
in a number of scenarios. Consider the following case:
1. Alice and Bob are both located in different networks with Network
Address Translation (NAT). Alice and Bob themselves have
different address but both networks use the same private internet
block (e.g., the "20-bit block" 172.16/12 specified in
[RFC1918]).
2. Alice conveys to Bob the candidate 172.16.0.1 which also happens
to correspond to an existing host on Bob's network.
3. Bob creates a check list consisting solely of 172.16.0.1 and
starts checks.
4. These checks reach the host at 172.16.0.1 in Bob's network, which
responds with an ICMP "port unreachable" error; per [rfc5245bis]
Bob marks the transaction as Failed.
At this point the check list only contains Failed candidates and the
valid list is empty. This causes the data stream and potentially all
ICE processing to fail, even though if Trickle ICE agents could
subsequently convey candidates that would cause previously empty
check lists to become non-empty.
A similar race condition would occur if the initial ICE description
from Alice contain only candidates that can be determined as
unreachable from any of the candidates that Bob has gathered (e.g.,
this would be the case if Bob's candidates only contain IPv4
addresses and the first candidate that he receives from Alice is an
IPv6 one).
Another potential problem could arise when a non-trickle ICE
implementation initiates an interaction with a Trickle ICE
implementation. Consider the following case:
1. Alice's client has a non-Trickle ICE implementation.
2. Bob's client has support for Trickle ICE.
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3. Alice and Bob are behind NATs with address-dependent filtering
[RFC4787].
4. Bob has two STUN servers but one of them is currently
unreachable.
After Bob's agent receives Alice's initial ICE description it would
immediately start connectivity checks. It would also start gathering
candidates, which would take a long time because of the unreachable
STUN server. By the time Bob's answer is ready and conveyed to
Alice, Bob's connectivity checks might have failed: until Alice gets
Bob's answer, she won't be able to start connectivity checks and
punch holes in her NAT. The NAT would hence be filtering Bob's
checks as originating from an unknown endpoint.
Appendix B. Interaction with ICE Lite
The behavior of ICE lite agents that are capable of Trickle ICE does
not require any particular rules other than those already defined in
this specification and [rfc5245bis]. This section is hence provided
only for informational purposes.
An ICE lite agent would generate candidate information as per
[rfc5245bis] and would indicate support for Trickle ICE. Given that
the candidate information will contain a full generation of
candidates, it would also be accompanied by an end-of-candidates
indication.
When performing full trickle, a full ICE implementation could convey
the initial ICE description or response thereto with no candidates.
After receiving a response that identifies the remote agent as an ICE
lite implementation, the initiator can choose to not trickle any
additional candidates. The same is also true in the case when the
ICE lite agent initiates the interaction and the full ICE agent is
the responder. In these cases the connectivity checks would be
enough for the ICE lite implementation to discover all potentially
useful candidates as peer reflexive. The following example
illustrates one such ICE session using SDP syntax:
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ICE Lite Bob
Agent
| Offer (a=ice-lite a=ice-options:trickle) |
|---------------------------------------------->|
| |no cand
| Answer (a=ice-options:trickle) |trickling
||
peer rflx| |
cand disco| |
|<========== CONNECTION ESTABLISHED ===========>|
Figure 8: Example
In addition to reducing signaling traffic this approach also removes
the need to discover STUN bindings or make TURN allocations, which
can considerably lighten ICE processing.
Appendix C. Changes from Earlier Versions
Note to the RFC Editor: please remove this section prior to
publication as an RFC.
C.1. Changes from draft-ietf-ice-trickle-20
o Slight corrections to hanlding of peer reflexive candidates.
o Wordsmithing in a few sections.
C.2. Changes from draft-ietf-ice-trickle-19
o Further clarified handling of remote peer reflexive candidates.
o To improve readibility, renamed and restructured some sections and
subsections, and modified some wording.
C.3. Changes from draft-ietf-ice-trickle-18
o Cleaned up pairing and redundancy checking rules for newly
discovered candidates per IESG feedback and WG discussion.
o Improved wording in half trickle section.
o Changed "not more than once" to "exactly once".
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o Changed NAT examples back to IPv4.
C.4. Changes from draft-ietf-ice-trickle-17
o Simplified the rules for inserting a new pair in a check list.
o Clarified it is not allowed to nominate a candidate pair after a
pair has already been nominated (a.k.a. renomination or
continuous nomination).
o Removed some text that referenced older versions of rfc5245bis.
o Removed some text that duplicated concepts and procedures
specified in rfc5245bis.
o Removed the ill-defined concept of stream order.
o Shortened the introduction.
C.5. Changes from draft-ietf-ice-trickle-16
o Made "ufrag" terminology consistent with 5245bis.
o Applied in-order delivery rule to end-of-candidates indication.
C.6. Changes from draft-ietf-ice-trickle-15
o Adjustments to address AD review feedback.
C.7. Changes from draft-ietf-ice-trickle-14
o Minor modifications to track changes to ICE core.
C.8. Changes from draft-ietf-ice-trickle-13
o Removed independent monitoring of check list "states" of frozen or
active, since this is handled by placing a check list in the
Running state defined in ICE core.
C.9. Changes from draft-ietf-ice-trickle-12
o Specified that the end-of-candidates indication must include the
generation (ufrag/pwd) to enable association with a particular ICE
session.
o Further editorial fixes to address WGLC feedback.
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C.10. Changes from draft-ietf-ice-trickle-11
o Editorial and terminological fixes to address WGLC feedback.
C.11. Changes from draft-ietf-ice-trickle-10
o Minor editorial fixes.
C.12. Changes from draft-ietf-ice-trickle-09
o Removed immediate unfreeze upon Fail.
o Specified MUST NOT regarding ice-options.
o Changed terminology regarding initial ICE parameters to avoid
implementer confusion.
C.13. Changes from draft-ietf-ice-trickle-08
o Reinstated text about in-order processing of messages as a
requirement for signaling protocols.
o Added IANA registration template for ICE option.
o Corrected Case 3 rule in Section 8.1.1 to ensure consistency with
regular ICE rules.
o Added tabular representations to Section 8.1.1 in order to
illustrate the new pair rules.
C.14. Changes from draft-ietf-ice-trickle-07
o Changed "ICE description" to "candidate information" for
consistency with 5245bis.
C.15. Changes from draft-ietf-ice-trickle-06
o Addressed editorial feedback from chairs' review.
o Clarified terminology regarding generations.
C.16. Changes from draft-ietf-ice-trickle-05
o Rewrote the text on inserting a new pair into a check list.
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C.17. Changes from draft-ietf-ice-trickle-04
o Removed dependency on SDP and offer/answer model.
o Removed mentions of aggressive nomination, since it is deprecated
in 5245bis.
o Added section on requirements for signaling protocols.
o Clarified terminology.
o Addressed various WG feedback.
C.18. Changes from draft-ietf-ice-trickle-03
o Provided more detailed description of unfreezing behavior,
specifically how to replace pre-existing peer-reflexive candidates
with higher-priority ones received via trickling.
C.19. Changes from draft-ietf-ice-trickle-02
o Adjusted unfreezing behavior when there are disparate foundations.
C.20. Changes from draft-ietf-ice-trickle-01
o Changed examples to use IPv6.
C.21. Changes from draft-ietf-ice-trickle-00
o Removed dependency on SDP (which is to be provided in a separate
specification).
o Clarified text about the fact that a check list can be empty if no
candidates have been sent or received yet.
o Clarified wording about check list states so as not to define new
states for "Active" and "Frozen" because those states are not
defined for check lists (only for candidate pairs) in ICE core.
o Removed open issues list because it was out of date.
o Completed a thorough copy edit.
C.22. Changes from draft-mmusic-trickle-ice-02
o Addressed feedback from Rajmohan Banavi and Brandon Williams.
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o Clarified text about determining support and about how to proceed
if it can be determined that the answering agent does not support
Trickle ICE.
o Clarified text about check list and timer updates.
o Clarified when it is appropriate to use half trickle or to send no
candidates in an offer or answer.
o Updated the list of open issues.
C.23. Changes from draft-ivov-01 and draft-mmusic-00
o Added a requirement to trickle candidates by order of components
to avoid deadlocks in the unfreezing algorithm.
o Added an informative note on peer-reflexive candidates explaining
that nothing changes for them semantically but they do become a
more likely occurrence for Trickle ICE.
o Limit the number of pairs to 100 to comply with 5245.
o Added clarifications on the non-importance of how newly discovered
candidates are trickled/sent to the remote party or if this is
done at all.
o Added transport expectations for trickled candidates as per Dale
Worley's recommendation.
C.24. Changes from draft-ivov-00
o Specified that end-of-candidates is a media level attribute which
can of course appear as session level, which is equivalent to
having it appear in all m-lines. Also made end-of-candidates
optional for cases such as aggressive nomination for controlled
agents.
o Added an example for ICE lite and Trickle ICE to illustrate how,
when talking to an ICE lite agent doesn't need to send or even
discover any candidates.
o Added an example for ICE lite and Trickle ICE to illustrate how,
when talking to an ICE lite agent doesn't need to send or even
discover any candidates.
o Added wording that explicitly states ICE lite agents have to be
prepared to receive no candidates over signaling and that they
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should not freak out if this happens. (Closed the corresponding
open issue).
o It is now mandatory to use MID when trickling candidates and using
m-line indexes is no longer allowed.
o Replaced use of 0.0.0.0 to IP6 :: in order to avoid potential
issues with RFC2543 SDP libraries that interpret 0.0.0.0 as an on-
hold operation. Also changed the port number here from 1 to 9
since it already has a more appropriate meaning. (Port change
suggested by Jonathan Lennox).
o Closed the Open Issue about use about what to do with cands
received after end-of-cands. Solution: ignore, do an ICE restart
if you want to add something.
o Added more terminology, including trickling, trickled candidates,
half trickle, full trickle,
o Added a reference to the SIP usage for Trickle ICE as requested at
the Boston interim.
C.25. Changes from draft-rescorla-01
o Brought back explicit use of Offer/Answer. There are no more
attempts to try to do this in an O/A independent way. Also
removed the use of ICE Descriptions.
o Added SDP specification for trickled candidates, the trickle
option and 0.0.0.0 addresses in m-lines, and end-of-candidates.
o Support and Discovery. Changed that section to be less abstract.
As discussed in IETF85, the draft now says implementations and
usages need to either determine support in advance and directly
use trickle, or do half trickle. Removed suggestion about use of
discovery in SIP or about letting implementing protocols do what
they want.
o Defined Half Trickle. Added a section that says how it works.
Mentioned that it only needs to happen in the first o/a (not
necessary in updates), and added Jonathan's comment about how it
could, in some cases, offer more than half the improvement if you
can pre-gather part or all of your candidates before the user
actually presses the call button.
o Added a short section about subsequent offer/answer exchanges.
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o Added a short section about interactions with ICE Lite
implementations.
o Added two new entries to the open issues section.
C.26. Changes from draft-rescorla-00
o Relaxed requirements about verifying support following a
discussion on MMUSIC.
o Introduced ICE descriptions in order to remove ambiguous use of
3264 language and inappropriate references to offers and answers.
o Removed inappropriate assumption of adoption by RTCWEB pointed out
by Martin Thomson.
Authors' Addresses
Emil Ivov
Atlassian
303 Colorado Street, #1600
Austin, TX 78701
USA
Phone: +1-512-640-3000
Email: eivov@atlassian.com
Eric Rescorla
RTFM, Inc.
2064 Edgewood Drive
Palo Alto, CA 94303
USA
Phone: +1 650 678 2350
Email: ekr@rtfm.com
Justin Uberti
Google
747 6th St S
Kirkland, WA 98033
USA
Phone: +1 857 288 8888
Email: justin@uberti.name
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Peter Saint-Andre
Mozilla
P.O. Box 787
Parker, CO 80134
USA
Phone: +1 720 256 6756
Email: stpeter@mozilla.com
URI: https://www.mozilla.com/
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